Tropical and mid-latitude 45-day perturbations over the Western Pacific during the northern summer
Tropical and mid-latitude 45-day perturbations over the Western Pacific during the northern summer
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DOI：
10.2151/jmsj1965.74.6_867
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发表时间：
1996
影响因子：
3.1
通讯作者：
R. Kawamura;T. Murakami;Bin Wang
中科院分区：
文献类型：
--
作者：
R. Kawamura;T. Murakami;Bin Wang
热带Madden-Julian涛动（MJO）在西北太平洋夏季风区（5° ~ 20 ° N，110° ~ 160 ° E）系统性地向北传播。向北传播的MJO具有显著的水平和垂直不对称环流特征。低层气旋响应是明显的，由于存在的收敛，气旋剪切平均季风流，而上层反气旋对应弱，由于发散，反气旋剪切上层平均季风流的影响。对流层上部的MJO响应在很大程度上与辐散风有关，这表现在向赤道方向的强外流将反气旋涡度输出到南半球对流层上部。夏季平均季风气流是负责加强对流加热引起的MJO环流的垂直不对称性，并通过平均季风气流-MJO相互作用在斜压MJO中产生正压分量。中纬度季节内振荡（ISO）表现为沿沿着横贯北太平洋的大圆的正压波列结构，在北太平洋西风急流出口区（40° ~ 50 ° N，180° ~ 150 ° W）的变率最大。这一现象是两种不同的动力学过程结合的结果。当MJO向北传播时，由平均季风流-MJO相互作用产生的正压MJO分量在季节内时间尺度上产生了显著的热带-热带外相互作用。也就是说，当菲律宾附近45天的对流活动变得最强时，正压MJO分量成为对流强迫产生的正压Rossby波频散的起源，最终导致温带ISO的发展。涡度拟能收支分析表明，另一方面，ISO的最大贡献是在原地正压平均流ISO的相互作用和周围的射流出口。
The tropical Madden-Julian oscillation (MJO), which is of convective origin, systematically propagates northward in the Western North Pacific summer monsoon region (5°-20°N, 110°-160°E). The northward propagating MJO, which is statistically significant, displays strong horizontally and vertically asymmetric circulation. The low-level cyclonic response is pronounced due to the presence of convergent, cyclonically sheared mean monsoon flow, while the upper-level anticyclonic counterpart is weak due to the influence of the divergent, anticyclonically sheared upper-level mean monsoon flow. The upper tropospheric MJO response is largely associated with divergent winds, as manifested by strong equatorward outflows that export anticyclonic vorticity into the upper troposphere of the Southern Hemisphere. The summer mean monsoon flow is responsible for reinforcing the vertical asymmetry of the MJO circulation induced by convective heating, and for generating a barotropic component in the baroclinic MJO through the mean monsoon flow-MJO interaction. The mid-latitude intraseasonal oscillation (ISO) displays a barotropic wave train structure along a great circle traversing the North Pacific, and exhibits the largest variability in the westerly jet exit region of the North Pacific (40°-50°N, 180°-150°W). This phenomenon is attributed to the combination of two different dynamic processes. While the MJO is propagating northward, the barotropic MJO component generated by the mean monsoon flow-MJO interaction produces a significant tropical-extratropical interaction on the intraseasonal time scale. Namely, when the 45-day convective activity becomes strongest near the Philippines, the barotropic MJO component acts as an origin of the barotropic Rossby wave dispersion emanating out of the convective forcing, eventually contributing to the development of an extratropical ISO. The enstrophy budget analysis shows, on the other hand, that the largest contribution to ISO is the in situ barotropic mean flow-ISO interaction in and around the jet exit.